A distractible spinal implant composed of two U-shaped parts is known from U.S. Pat. No. 7,029,498 B2 in which the two parts are held so that they are axially displaceable against each other in the manner of a telescope. On the free webs of the U-shaped outer part, a transport admission is formed, into which a gripping forceps is insertable. The attending physician can grasp the spinal implant with this gripping forceps and transport it to the desired location.
Once the spinal implant is positioned, the grasping forceps is removed. In order to distract the spinal implant to the desired size, an oblong guidance rod is then led past the opening of the U-shaped part into the inside of the spinal implant and screwed into a thread available on the outer part before pushing a hollow toothed instrument over the guidance rod. The toothed instrument is thereby pushed into the spinal implant until outer teeth provided on the toothed instrument engage with correspondingly formed teeth on the inner part of the spinal implant. If one now rotates the toothed instrument about its longitudinal axis, the inner part of the spinal implant is displaced relative to the outer part.
This entire process is very difficult and requires a high degree of dexterity on the part of the surgeon. Since the toothed instrument sits only very loosely on the guidance rod, it can happen that during distraction it accidentally slips out of the engagement with the teeth, so that it needs to be inserted again.